Scintillator panel, radiation image sensor and methods of producing them

ABSTRACT

Scintillator panel  1  comprises a radiation transmitting substrate  5,  which has heat resistance, a dielectric multilayer film mirror  6,  as a light reflecting film and is formed on the radiation transmitting substrate  5,  and a scintillator  10,  disposed on the dielectric multilayer film mirror  6  and emits light by conversion of the radiation  30  that has been made to enter the radiation transmitting substrate  5  and has passed through the dielectric multilayer film mirror  6.  Since the radiation transmitting substrate  5  has heat resistance, the dielectric multilayer film mirror  6  can be vapor deposited at a high temperature and, as a result, can be formed in a state of high reflectance. Also, unlike a metal film, the dielectric multilayer film mirror  6  will not corrode upon reacting with the scintillator  10.

DESCRIPTION

[0001] 1. Technical Field

[0002] This invention relates to a scintillator panel to be used forradiation imaging for medical use, etc., a radiation image sensor thatmakes use of this scintillator panel, and methods for making theseitems.

[0003] 2. Background Art

[0004] Radiation image sensors, which convert radiation into electricalsignals and enable electrical processing of the signals, are used widelyin medical and industrial fields. The acquired electrical signals can beprocessed electrically and displayed on a monitor. A representativeexample of such a radiation image sensor is a radiation image sensorthat uses a scintillator material for converting radiation in to light.With this type of radiation image sensor, an image pickup device, forfurther conversion of the converted light into electrical signals, isused in combination. For example, a MOS type image sensor, etc., is usedas the image pickup device. For use in medical fields andnon-destructive inspections (especially inspections using amicro-focused X-ray source, etc.), the irradiation dose of radiation islimited, and thus a radiation image sensor of high sensitivity thatenables a high optical output with the limited irradiation dose isdesired.

[0005]FIG. 9 is a longitudinal sectional view of a radiation imagesensor described in International Patent Publication No. WO99/66345(referred to hereinafter as “Prior Art 1”). To form this radiation imagesensor 4, a scintillator panel 8, comprising a substrate 50, a lightreflecting film 60, formed on the substrate 50, and a scintillator 10,formed on the light reflecting film 60, is combined with an image pickupdevice 20, which is disposed so as to face the scintillator 10.Radiation 30 enters from the substrate 50 side, passes through the lightreflecting film 60, and is converted into light at the scintillator 10.The light resulting from conversion is received by the image pickupdevice 20 and converted into electrical signals. The light reflectingfilm 60 has a function of reflecting the light emitted by thescintillator 10 and returning this light to the scintillator 10 side tothereby increase the amount of light entering the light receiving partof the image pickup device 20. A film of metal, such as aluminum, etc.,is mainly used as the light reflecting film 60.

[0006]FIG. 10 is a longitudinal sectional view of a radiation imagingdevice described in JP 5-196742A (referred to hereinafter as “Prior Art2”). This radiation imaging device 3 comprises a substrate 51, a lightdetector 21, which is disposed on the substrate 51 and serves as animage pickup device, a scintillator 10, formed on the light detector 21,a thin film 41, disposed on the scintillator 10, a light reflecting film70, formed on the thin film 41, and a moisture sealing layer 42, formedon the light reflecting film 70. This arrangement differs largely fromthat of the Prior Art 1 in that the light detector 21 is used as a basemember for fixing and supporting the scintillator 10 and the lightreflecting film 70 is formed above the scintillator 10 across the thinfilm 41. The thin film 41 is formed of an organic or inorganic materialand absorbs the non-uniformity on the scintillator 10 to make the lightreflecting film 70 uniform in reflectance. This publication indicatesthat a dielectric multilayer film, arranged from TiO₂ and SiO₂, etc.,which differ mutually in optical refractive index, may be used as thelight reflecting film 70.

[0007] Disclosure of the Invention

[0008] These prior-art radiation image sensors had the followingproblems. That is, with the Prior Art 1, though a metal film is used asthe light reflecting film 60, in many cases, this metal film 60 reactswith the scintillator 10 and undergoes corrosion. Such corrosion becomessignificant especially in a case where CsI (Tl) is used as thescintillator 10.

[0009] With the Prior Art 2, a dielectric multilayer film is used aslight reflecting film 70, and since the scintillator 10 has a structurewherein a plurality of microscopic, columnar crystals, each with adiameter of approximately several μm to several dozen μm, are arrangedin the form of bristles and thus has minute unevenness on the surface,it is difficult to directly form the dielectric multilayer 70 on such anuneven surface. The thin film 41 is thus interposed to flatten thisunevenness. In order to form the dielectric multilayer film 70 to astate in which it is provided with a high reflectance, vapor depositionmust be performed upon heating the base on which the multilayer film isto be formed to approximately 300° C. However, it is difficult to evensimply apply a high temperature in a case where the thin film 41 is anorganic film. Though it is possible to form a multilayer film at atemperature of no more than 300° C., it is difficult to control thethickness of the film that is formed and the problem that the dielectricmultilayer film 70 becomes formed in a colored state occurs, causing thereflectance to drop and the optical output to decrease. In a case wherethe thin film 41 is formed of an inorganic film, it is difficult to forma flat surface for forming the multilayer film on the scintillator withan inorganic film, and as a result, the dielectric multilayer filmbecomes uneven on the surface (reflecting surface) and cannot beprovided with high reflectance.

[0010] Thus an object of this invention is to provide a scintillatorpanel and a radiation image sensor, which is excellent in corrosionresistance and yet can provide a high optical output, and methods formaking such a scintillator panel and radiation image sensor.

[0011] In order to achieve the above object, a scintillator panelaccording to the present invention is characterized in comprising: aheat-resistant substrate; a dielectric multilayer film mirror, depositedon the heat-resistant substrate; a scintillator, deposited so as toarrange a plurality of columnar structures on the dielectric multilayerfilm mirror and converting incident radiation into light; and aprotective film, covering at least the scintillator; and wherein thedielectric multilayer film mirror reflects light emitted from thescintillator and returns this light toward the scintillator.

[0012] Since the dielectric multilayer film mirror is formed on theheat-resistant substrate, it is not necessary to form a thin film etc.for making the reflectance uniform in a case where the dielectricmultilayer film mirror is formed on the scintillator, such as a filmthat absorbs the non-uniformity on the scintillator. And since thesubstrate is heat resistant, vapor deposition at a high temperature canbe performed to enable the forming of a dielectric multilayer filmmirror of high reflectance.

[0013] Furthermore, the substrate may be a radiation transmittingsubstrate and the scintillator may emit light by conversion of theradiation that has passed through the dielectric multilayer film mirror.In this case, the scintillator preferably has CsI or NaI as the maincomponent. The scintillator may also be photostimulable phosphor.

[0014] The protective film is preferably an organic film. In this case,the protective film does not need to be formed at a high temperature andthus is readily formable.

[0015] As the dielectric multilayer film mirror, a multilayer filmhaving laminated structure with alternating TiO₂ or Ta₂O₅ and SiO₂layers is preferably adopted. This is because in the case of TiO₂ orTa₂O₅ and SiO₂, corrosion upon reaction with the scintillator, whichoccurs with a metal reflecting film, will not occur and good reflectioncharacteristics can be obtained over a wide wavelength range.

[0016] A separation preventing layer, which prevents the separation ofthe scintillator from the dielectric multilayer film mirror, ispreferably disposed between the dielectric multilayer film mirror andthe scintillator. The separation preventing layer may be a polyimidelayer.

[0017] A radiation image sensor according to the present inventioncomprises: the above-described scintillator panel; and an image pickupdevice, disposed so as to face the scintillator panel and converting thelight emitted by the scintillator to electrical signals. A radiationimage sensor provided with a scintillator panel of good corrosionresistance and high reflectance, can thus be realized to enable thelight emitted by this scintillator panel to be processed electricallyand displayed on a monitor, etc.

[0018] Furthermore, by providing a light-absorbing housing that coversthe scintillator panel, the generation of stray light due to scatteringof the light that has passed through the dielectric multilayer filmmirror and the generation of noise due to the entry of extraneous lightcan be restrained to enable a high S/N ratio and high resolution to beachieved. This housing is preferably made of polycarbonate and its innersurface is preferably matte furnished.

[0019] Furthermore, putting the scintillator panel into adhesion withthe image pickup device by means of fixing jigs is even more preferableas this will restrain the leakage of light and the occurrence ofcross-talk.

[0020] A method of making a scintillator panel according to the presentinvention comprises the steps of: preparing a heat-resistant substrate;repeatedly depositing a dielectric film of desired thickness onto thesubstrate to form a dielectric multilayer film mirror with predeterminedreflection characteristics; depositing columnar structures of ascintillator on the dielectric multilayer film mirror; and coating thescintillator with a protective film.

[0021] A method for making a radiation image sensor according to thepresent invention further comprises a step of positioning an imagepickup device so as to face the scintillator manufactured by theabovementioned steps. A step of covering the scintillator panel with alight-absorbing housing may also be provided.

[0022] The scintillator panel and radiation image sensor according tothe present invention can be made favorably by these making methods.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a longitudinal sectional view of a first embodiment of ascintillator panel according to the present invention.

[0024]FIG. 2A to FIG. 2F are diagrams for explaining the steps formaking the scintillator panel of FIG. 1.

[0025]FIG. 3 is a longitudinal sectional view of a first embodiment of aradiation image sensor according to the present invention.

[0026]FIG. 4 is an enlarged sectional view for explaining the operationof the radiation image sensor of FIG. 3.

[0027]FIG. 5 and FIG. 6 are longitudinal sectional views for explaininga second embodiment of a scintillator panel according to the presentinvention.

[0028]FIG. 7 and FIG. 8 are longitudinal sectional views for explainingsecond and third embodiments of a radiation image sensor according tothe present invention.

[0029]FIG. 9 and FIG. 10 are longitudinal sectional views of prior-arttype radiation image sensors.

BEST MODES FOR CARRYING OUT THE INVENTION

[0030] Favorable embodiments of this invention shall now be described indetail with reference to the attached drawings. To facilitate thecomprehension of the explanation, the same reference numerals denote thesame parts, where possible, throughout the drawings, and a repeatedexplanation will be omitted.

[0031]FIG. 1 is a longitudinal sectional view of a first embodiment of ascintillator panel according to the present invention. The scintillatorpanel 1 comprises a Pyrex glass substrate 5 as a radiation transmittingsubstrate with heat resistance, a dielectric multilayer film mirror 6,formed on the Pyrex glass substrate 5, a polyimide layer 7, formed onthe dielectric multilayer film mirror 6 as a separation preventinglayer, and a scintillator 10, formed on the polyimide layer 7 andemitting light converted from the radiation 30 that has entered thePyrex glass substrate 5 and has passed through the dielectric multilayerfilm mirror 6 and the separation preventing layer 7. The scintillator 10has a structure wherein a plurality of microscopic columnar crystals,each with a diameter of a few μm to a few dozen μm, are arranged in theform of bristles. The entirety of these is covered by a polyparaxylylenefilm 12 as a protective film. A thin film of SiN, etc., may be providedbetween the Pyrex glass substrate 5 and the dielectric multilayer filmmirror 6. This thin layer is useful to make the glass substrate surfacea uniform, clean surface. As the dielectric multilayer film mirror 6,for example a multilayer film, wherein TiO₂ and SiO₂, which differmutually in optical refractive index, are alternately laminatedrepeatedly a plurality of times, is used, and this film mirror acts as alight reflecting film that reflects and amplifies the light emitted bythe scintillator 10. Tl-doped CsI is used for example for thescintillator 10.

[0032] When a scintillator, having a structure wherein a plurality ofcolumnar crystals are arranged in the form of bristles, is to be formed,a base member that fixes and supports the scintillator is necessary, inthe present embodiment, the Pyrex glass substrate 5 is used as the basemember that fixes and supports the scintillator 10. Though it ispossible to form the scintillator 10 using an image pickup device as thebase member, in this case, the image pickup device will be subject toheat repeatedly in the process of forming the scintillator 10 as well asin the process of forming the dielectric multilayer film mirror 6 andcan thus become damaged. According to the present embodiment, since thescintillator 10 is formed on the Pyrex glass substrate 5, such a problemis resolved. Also, since this Pyrex glass substrate 5 is heat resistant,vapor deposition at a high temperature close to 300° C. is enabled andthis enables the dielectric multilayer film mirror 6 to be formed to astate wherein it has a high reflectance.

[0033] Also, the dielectric multilayer film is excellent in corrosionresistance and thus will not corrode upon reacting with the scintillator10 as in the case of a metal film. The corrosion in the case of a metalfilm is considered to corrosion of the metal film by Tl in the CsI withthe moisture ingress into the interior of the scintillator panel andthis required devising a structure for preventing the moisture ingressinto the panel interior. However, according to the present embodiment,this requirement is eliminated by the use of the dielectric multilayerfilm mirror 6 of high corrosion resistance.

[0034] Furthermore, since the polyimide layer 7 is provided as aseparation preventing layer between the dielectric multilayer filmmirror 6 and the scintillator 10, the separation of the scintillator 10from the dielectric multilayer film 6, which may occur when thethickness of the scintillator 10 is increased (especially to 400 μm ormore), is prevented.

[0035] The steps for making this scintillator panel 1 shall now bedescribed. First, as the radiation transmitting substrate 5, a Pyrexglass substrate 5 of 20 cm square and 0.5 mm thickness is prepared (seeFIG. 2A), and TiO₂ 6₁, 6₃, . . . 6₄₁ and SiO₂ 6₂, 6₄, . . . 6₄₂ arelaminated alternately and repeatedly onto this Pyrex substrate 5 byvacuum vapor deposition (see FIG. 2B and FIG. 2C) to form a dielectricmultilayer film mirror 6 comprising a total of 42 layers (totalthickness: approximately 4 μm) (see FIG. 2D). By controlling the filmthickness of each layer, a predetermined reflectance for a predeterminedwavelength range can be secured for the dielectric multilayer filmmirror 6 as a whole.

[0036] As the radiation transmitting substrate 5, besides a Pyrex glasssubstrate, an amorphous carbon plate or an aluminum plate may be used.In the case of an aluminum plate, the dielectric multilayer film mirror6 is formed after performing sandblasting using glass beads (#1500) toremove rolling scars on the aluminum surface. On the dielectricmultilayer film mirror 6, a highly transparent polyimide layer (forexample, type name RN-812, made by Nissan Chemical Industries, Ltd.), asa separation preventing layer 7, is cured and then coated to a filmthickness of 1 μm by spin coating (see FIG. 2E). Thereafter, columnarcrystals of CsI of a thickness of 300 μm are formed by vapor depositionas a scintillator 10 on the polyimide layer 7 (see FIG. 2F). Then inorder to flatten foreign matter and anomalous growth parts on the CsIsurface, a glass plate is placed on the CsI surface and pressure isapplied at a force of 1 atmosphere. Lastly, a polyparaxylylene film 12of 10 μm thickness is formed by CVD as a protective film that covers theentirety, and the scintillator panel 1 shown in FIG. 1 is thus formed.

[0037] In a case where a scintillator panel 1 with a large area of 30 cmsquare or more is to be formed, the polyimide layer 7 is formed to athickness of 1 μm and screen printing is used as the coating method.Also in order to improve the luminance in accompaniment with increasedsize, the scintillator 10 is made 500 μm in thickness.

[0038]FIG. 3 is a longitudinal sectional view of a radiation imagesensor 2 according to the present invention. This radiation image sensor2 is arranged by combining an image pickup device 20 with thescintillator 10 of the scintillator panel 1 shown in FIG. 1 bypositioning the image pickup device 20 so as to face the scintillator10. The image pickup device 20 converts the light emitted by thescintillator 10 into electrical signals. For example, a MOS type imagesensor having two-dimensionally aligned Si photodiodes is used as theimage pickup device 20.

[0039]FIG. 4 is an enlarged sectional view for explaining the operationof the radiation image sensor 2. Radiation 30, which has not beenblocked by or has been transmitted through a subject, 32, passes throughthe polyparaxylylene film 12, Pyrex glass substrate 5, dielectricmultilayer film mirror 6, and polyimide layer 7 and enters thescintillator 10. The scintillator 10 converts the incident radiation 30into light and emits this light. Part of the light emitted from thescintillator 10 proceeds towards the dielectric multilayer film mirror 6and this light is reflected by the dielectric multilayer film mirror 6and is returned to the scintillator 10. Most of the light that isemitted is thus directed towards and received by the image pickup device20. The image pickup device 20 converts the received light imageinformation into electrical signals and outputs these signals. Theelectrical signals that are thus output are sent to and displayed on amonitor, etc., as image signals, and since the image here is oneresulting from the conversion of a radiation image that entered theradiation image sensor 2 into a light image by the scintillator 10 andfurther conversion into electrical image signals by the image pickupdevice 20, it corresponds to being the subject 32's radiation image thatentered the image sensor.

[0040] As described above, since the dielectric multilayer film mirror 6of this embodiment has a high reflectance, the scintillator panel 1 andthe radiation image sensor 2 that use this dielectric multilayer filmmirror 6 are high in optical output.

[0041] In order to evaluate the sensitivity to radiation 30 and thecorrosion resistance of the radiation image sensor 2 having thescintillator panel 1 prepared in the above-described manner, threesamples (referred to respectively as “Examples 1 to 3”) were prepared asexamples of this invention and two samples (referred to respectively as“Prior-Art Examples 1 and 2”) of the prior-art type radiation imagesensors were prepared with respectively different arrangements. Table 1shows the arrangements of these samples. TABLE 1 Arrangements of thecompared samples Arrangement Light Separation Sample Substratereflecting film preventing layer Prior-Art Pyrex glass Aluminum filmNone Example 1 Prior-Art Amorphous Silver film Example 2 carbon Example1 Pyrex glass Example 2 Amorphous Dielectric Polyimide carbon multilayerfilm Example 3 Aluminum plate

[0042] With each of the samples, CsI was used for the scintillator, apolyparaxylylene film was used as the protective film, and C-MOS wasused for the image pickup device.

[0043] As a test for evaluating the sensitivity with respect toradiation 30, a fixed amount of radiation 30 was irradiated onto each ofthe samples and the optical output values were measured. As a test forevaluating the corrosion resistance, a shelf test over several days wasconducted on just the scintillator panels from which the image pickupdevices 20 had been removed. The results of these tests are shown inTable 2. The optical output values are indicated as relative values withthat of the Prior-Art Example 1 being set to 100%. TABLE 2 Test Resultsof the Samples Test item Relative Sample output value Corrosionresistance Prior-Art 100% The Al film corroded upon being left Example 1for 1 to 2 days under 40° C. air temperature and 90% humidity. Prior-Art140% The Ag film corroded upon being left Example 2 for 1 to 2 daysunder room temperature and room humidity. Example 1 140% No changes.Example 2 130% No changes. Example 3 135% No changes.

[0044] Each of the Examples 1 to 3 were higher in optical output valuethan the Prior-Art Example 1 in which an aluminum film is used as thelight reflecting film and was approximately equal in optical outputvalue to the Prior-Art Example 2 in which a silver film is used. Withregard to the corrosion resistance test, whereas corrosion occurred in 1to 2 days with the Prior-Art Examples 1 and 2 that use metal films,changes were not seen with the Examples 1 to 3 that use dielectricmultilayer film mirrors 6.

[0045] Also, the following test was conducted in order to check theeffects of separation preventing layer 7. As samples, ten Pyrex glass(PX) substrates of 50 mm square and 1 mm thickness, each having 27layers of the dielectric multilayer film mirror laminated thereon, wereprepared. From each of these samples, five samples with polyimide layer7 being coated onto the dielectric multilayer film mirror 6 as theseparation preventing layer and five samples without coating wereprepared, and with all samples, scintillator CsI was deposited. Witheach sample, ten layers of CsI were deposited, and the thickness wasvaried in five stages. The number of samples for which the separation ofCsI occurred was examined. TABLE 3 Occurrence of separation of CsI withrespect to thickness of CsI and existence of polyimide layer Thicknessof CsI 100 μm 200 μm 300 μm 400 μm 500μm Without polyimide layer 0/100/10 0/10 3/10 8/10 With polyimide layer 0/10 0/10 0/10 0/10 0/10

[0046] As indicated clearly in Table 3, whereas in the case of samplesthat do not use the polyimide layer 7 on the dielectric multilayer filmmirror 6, separation began to occur at the point at which the thicknessof the CsI exceeded 400 μm, separation of CsI was not seen with samplesusing the polyimide layer 7. This test also showed that in a case wherethe scintillator 10 is doped with Tl in the form of CaI(Tl) or NaI(Tl),the polyimide layer 7 simultaneously prevents the problem that the Tldiffuses slightly into and colors the dielectric multilayer film mirror6 in the process of forming the scintillator by vapor deposition.

[0047] The above test results confirm that this embodiment'sscintillator panel 1 and radiation image sensor 2 output a high opticaloutput, are excellent in corrosion resistance, and also exhibit theeffect of prevention of separation of the scintillator.

[0048] Other embodiments of this invention's scintillator panel andradiation image sensor shall now be described in detail.

[0049]FIG. 5 is a longitudinal sectional view, showing a secondembodiment of a scintillator panel according to the present invention.This scintillator panel 1 a has nearly the same arrangement as thescintillator panel 1 of the first embodiment shown in FIG. 1. Thedifferences are that a dielectric multilayer film mirror 6 a, formed bylaminating Ta₂O₅/SiO₂, which has a high reflectance for light from thevisible light to the ultraviolet range, is used and a so-calledphotostimulable phosphor of CsBr:Eu, etc., is used as scintillator 10 a.

[0050] Unlike the scintillator panel 1 shown in FIG. 1, thisscintillator panel 1 a is used by irradiating radiation 30 from thescintillator 10 a side. The scintillator 10 a is excited by theradiation that enters in such a manner. Thereafter, by scannedillumination of a He—Ne laser beam 34 across the scintillator 10 a asshown in FIG. 6, light that is in accordance with the amount of theirradiated radiation 30 is emitted from the scintillator 10 a. Thisemitted light is detected by light detector 22 and converted intoelectrical signals to enable the acquisition of image signalscorresponding to the radiation image.

[0051] By thus using a photostimulable phosphor for scintillator 6 a,storing the radiation image temporarily, and reading out the image bylaser beam scanning, the need to prepare an image pickup device of largearea is eliminated and the acquisition of a large-area radiation image,such as an image obtained for chest imaging, etc., is facilitated.Besides the abovementioned CsBr:Eu, various phosphors, such as thosedisclosed in JP No. 3,130,633, may be used as the photostimulablephosphor. Also, the TiO₂/SiO₂ laminate used in the first embodiment oran HFO₂/SiO₂ laminate, etc., may be used for the dielectric multilayerfilm mirror.

[0052]FIG. 7 is a longitudinal sectional view, showing a secondembodiment of a radiation image sensor according to the presentinvention. With this radiation image sensor 2 a, the radiation imagesensor 2 shown in FIG. 3 is provided furthermore with a housing 25 thatcovers the entirety of scintillator panel 1. This housing 25 is made ofa material, for example, black polycarbonate, which has a radiationtransmitting property, protects the entirety, and blocks external light.Light that has been emitted by the scintillator 10 and has beentransmitted through the dielectric multilayer film mirror 6 and thePyrex glass substrate 5 is thus absorbed by the housing 25 to restrainthe light from returning to a position that differs from thescintillator 10 side position from which the light was emitted andthereby restrain the degradation of resolution due to such stray light.The entry of extraneous light that acts as noise from the exterior canalso be restrained and a high S/N ratio can be maintained.

[0053] Also, this housing 25 is provided in a condition where it is putin press-contact against the Pyrex glass substrate 5 of the scintillatorpanel 1, and the scintillator panel 1 is adhered closely to the imagepickup device 20 by this press-contacting action. The occurrence ofleakage of light, cross-talk, etc., in the process of recognizing thelight emitted by the scintillator 10 by the image pickup device 20 canthereby be prevented. In order to realize an even higher degree ofadhesion, a sponge or other elastic material may also be placed betweenthe Pyrex glass substrate 5 and the housing 25.

[0054] As mentioned above, the use of glass as the substrate of thescintillator panel 1 provides the advantage of enabling the forming of ascintillator panel that is thin and yet will not bend. The use of adielectric multilayer film as a light reflecting film provides theadvantage of enabling the forming of a light reflecting film withexcellent corrosion resistance and high reflectance. Though when ascintillator panel that incorporates both of these is formed,transmitted light, which causes lowering of contrast, will occur, withthe present embodiment, this transmitted light is absorbed by theprovision of the housing 25 which has a light absorbing property,thereby enabling the advantages of the two abovementioned components tobe put to use while resolving the problem that occurs when the twocomponents are used.

[0055]FIG. 8 is a longitudinal sectional view, showing a thirdembodiment of a radiation image sensor according to the presentinvention. With this embodiment (radiation image sensor 2 b), an imagepickup device 20 is fixed on a sensor substrate 22, on which driving andreading circuits are mounted, the image pickup device 20 is fixed inadhesion with a scintillator panel 1 by the fixing of the scintillatorpanel 1 onto the sensor substrate 22 by fixing jigs 23, and the entiretyis covered by a housing 25 made of black polycarbonate. Since thescintillator panel 1 is adhered closely to the image pickup device 20 bythe cooperative action of the fixing jigs 23 and the housing 25 a, theoccurrence of leakage of light, cross-talk, etc., in the process ofrecognizing the light emitted by the scintillator 10 by the image pickupdevice 20 can be prevented. Though in the Figure, there is a spacebetween the glass substrate 5 and the housing 25 a, these components mayadhered together. By this structure, the occurrence of light, which,upon transmission through the Pyrex glass substrate 5, is reflectedinside housing 25 and re-enters the Pyrex glass substrate 5 to give riseto the lowering of contrast and other degrading effects on the opticaloutput, can be restrained and the lowering of the resolution and the S/Nratio can be restrained.

[0056] With regard to the housings 25 and 25 a, in addition to makingthe housing itself from a light-absorbing member, the inner surface thatcontacts the Pyrex glass substrate 5 may be subject to matte furnishing,coating of a light-absorbing coat, or adhesion of a light-absorbingmember.

[0057] In order to evaluate the contrast ratio of a radiation imagesensor with such a housing, a sample (referred to as “Example A”) ofthis invention's embodiment and a sample (referred to as “ComparativeExample B”) of a prior-art type radiation image sensor were prepared asmutually different arrangements. Besides having or not having a housing,Example A and Comparative Example B are made the same in arrangement andwith both, a dielectric multilayer film mirror is formed on Pyrex glass,a scintillator of CsI is disposed on the film mirror, a polyparaxylylenefilm is used as the protective film, and a C-MOS type image pickupdevice is used as the image pickup device.

[0058] As a test for measuring the contrast ratio, radiation wasirradiated upon placing a lead object of 3 cm diameter and 0.5 mmthickness on the housing, the signal values acquired by the radiationimage sensor for a portion covered by the lead and for a portion exposedto radiation, respectively, were measured, and the ratio of these valueswas computed. As a result, in comparison to the Comparative Example B,the contrast was improved by 10% and a clearer image was acquired withthe Example A.

[0059] The abovementioned test results thus confirmed that thisembodiment's radiation image sensor enables the acquisition of imageswith sharp contrast.

[0060] From the invention thus described, it will be obvious that theinvention may be varied in many ways. Such variations are not to beregarded as a departure from the spirit and scope of the invention, andall such modifications as would be obvious to one skilled in the art areintended for inclusion within the scope of the following claims.

[0061] Industrial Applicability

[0062] The scintillator panel and radiation image sensor according tothe present invention can be used favorably for chest imaging and othermedical uses as well as for non-destructive inspection and otherindustrial applications.

1. A scintillator panel comprising: a heat-resistant substrate; adielectric multilayer film mirror, deposited on said heat-resistantsubstrate; a scintillator, deposited so as to arrange a plurality ofcolumnar structures on said dielectric multilayer film mirror andconverting incident radiation into light and emitting this light; and aprotective film, covering at least said scintillator; wherein saiddielectric multilayer film mirror reflects light emitted from saidscintillator and returns this light toward said scintillator.
 2. Ascintillator panel comprising: a radiation transmitting substrate withheat resistance; a dielectric multilayer film mirror, formed on saidradiation transmitting substrate; a scintillator, deposited so as toarrange a plurality of columnar structures on said dielectric multilayerfilm mirror and converting radiation, which has entered said radiationtransmitting substrate and has passed through said dielectric multilayerfilm mirror, into light and emitting this light; and a protective film,covering at least said scintillator; wherein said dielectric multilayerfilm mirror reflects light emitted from said scintillator and returnsthis light toward said scintillator.
 3. The scintillator panel accordingto claim 1 or 2, wherein said scintillator has CsI or NaI as the maincomponent.
 4. The scintillator panel according to claim 1, wherein thescintillator is a photostimulable phosphor.
 5. The scintillator panelaccording to any of claims 1 to 4, wherein said protective film is anorganic film.
 6. The scintillator panel according to any of claims 1 to5, wherein said dielectric multilayer film mirror is a multilayer filmhaving laminated structure with alternating TiO₂ or Ta₂O₅ and SiO₂layers.
 7. The scintillator panel according to any of claims 1 to 6,further comprising a separation preventing layer, which prevents theseparation of said scintillator from said dielectric multilayer filmmirror, disposed between said dielectric multilayer film mirror and saidscintillator.
 8. The scintillator panel according to claim 7, whereinthe separation preventing layer is a polyimide layer.
 9. A radiationimage sensor comprising: the scintillator panel according to any ofclaims 1 to 8; and an image pickup device, disposed so as to face saidscintillator panel and converting the light emitted by said scintillatorto electrical signals.
 10. The radiation image sensor according to claim9, further comprising a light-absorbing housing that covers saidscintillator panel.
 11. The radiation image sensor according to claim10, wherein said housing is made of polycarbonate.
 12. The radiationimage sensor according to claim 10 or 11, wherein the inner surface ofsaid housing is matte finished.
 13. The radiation image sensor accordingto any of claims 10 to 12, further comprising a fixing jigs that fix thescintillator panel in adhesion with said image pickup device.
 14. Amethod for making a scintillator panel comprising the steps of:preparing a heat-resistant substrate; repeatedly depositing a dielectricfilm of desired thickness onto said substrate to form a dielectricmultilayer film mirror with predetermined reflection characteristics;depositing columnar structures of scintillator on said dielectricmultilayer film mirror; and coating the scintillator with a protectivefilm.
 15. A method for making a radiation image sensor comprising thestep of positioning an image pickup device so as to face thescintillator subsequent the steps of claim
 14. 16. The method for makingthe radiation image sensor according to claim 15, further comprising thestep of covering the scintillator panel with a light-absorbing housingsubsequent the steps of claim 15.